Precursor to metabolite: Bupropion hydrobromide ER to Hydroxybupropion

Bupropion hydrobromide ER is converted to Hydroxybupropion by CYP2B6.

The pair

Bupropion hydrobromide ER — Extended-release bupropion hydrobromide for depression; same active drug in a different salt.
Hydroxybupropion — Bupropion's principal active metabolite; largely noradrenergic and present at higher concentrations than the parent.

Anything that inhibits or induces CYP2B6 shifts the balance between Bupropion hydrobromide ER and Hydroxybupropion.